Damage to a battery case of a sealed battery has a large effect on the battery performance. For this reason, various methods for inspecting battery cases in the battery manufacturing process have been proposed. For example, an inspection method is known in which an alternating current is caused to flow through a primary coil of a probe, which is located close to the surface of a battery case, and the battery case and the probe are then moved relative to each other, to thereby detect a damaged part on the surface of the battery case based on a change in one of the measured values of an impedance of an induced current generated on the surface of the battery case and a voltage induced in a secondary coil (see Patent Literature 1).